There are some existing techniques that add a two-dimensional code as part of a printed document to embed some information (e.g., character strings) in coded form. A reading device captures this two-dimensional code on the printed document and decodes the read data to reconstruct the original information such as character strings.
Data encryption may be used to conceal a particular part of image data or text data. When partially encrypted image data is printed on some medium, the encrypted information appears in a deformed fashion on the resulting printed medium. To obtain its original information, a reading device is used to capture and decode the encrypted part of the printed medium. Such data encryption is applied to, for example, a confidential portion of documents to reduce the risk of information leakage via printed media.
Some of the existing devices for reading two-dimensional codes and encrypted part (hereafter “coded portion”) are designed to identify which area to decode on the basis of markers located at four corners (or some of them) of a two-dimensional code or coded portion.    Japanese Laid-open Patent Publication No. 07-254037    Japanese Laid-open Patent Publication No. 2008-301044    Japanese Laid-open Patent Publication No. 2009-232233
There may be a need for printing a plurality of coded portions on a single medium. This need arises when, for example, confidential information is distributed in two or more sections of a document. In the case where those coded portions are closely located, the markers to be attached to one coded portion could overlap with other coded portions or other existing markers. Such overlaps would cause a reading device to fail in reconstructing the information for the following reasons: (1) unable to detect markers because of their mutual overlaps, or (2) unable to distinguish individual coded portions because markers are combined incorrectly.